Semi-continuous mesophilic anaerobic co-digestion of thermally pretreated scum

The objective of this study is to investigate the mesophilic, anaerobic, co-digestion of scum with thickened waste activated sludge (TWAS) and primary sludge (PS). Observations of the reactor waste show that higher pretreatment temperatures assist in scum integration and appear to limit coagulation and separation effects associated with digesting fats, oils and greases. The 0.40 kg VS/m3 · d scum loaded reactor with scum pretreated at 70 °C achieved the greatest improvement in biogas production over PS and TWAS co-digestion without scum addition. Based on cell viability analysis of the reactor waste, scum-containing reactors were shown to produce 48 and 39% more biogas per m3 of live cells; signifying that scum addition increased the activity of the microbial population embedded in the waste or caused a microbial shift in the waste towards more active communities.